I hate it when there's that one scene the pulls an anime off the open recommendation (to non-anime-watching people) list.

I hate it when an entire series, or a large chunk, could be resolved if someone just told the truth or had the courage to spit something out.

I hate big finales that end with not a single character really evolving in any way. Bonus point if it looked like the characters were evolving in some way during the build-up and revert back after the climax.

Related: I hate open endings that are left open for what I can only ascertain is a dare to not give the series another season.

I hate it when someone who treats the main character like shit for years suddenly becomes a love interest.

I hate fan-service-y animes that feel they need to cover all their fan-service bases. (You can't please everyone, you know?)

Example: I'm watching Demon King Daimao and this guy (The Demon King) doesn't even attempt hook up with one of the hundreds of girls throwing themselves at him... I mean WTF. It's an ever annoying trend and makes it look like all highschool guys (most oftenly) are a bunch of scared little kids. I don't know many guys that would have a supermodel laying in bed beside them, begging to get in their pants and would turn them down.

If I was in a school of nothing but super attractive babes throwing themselves at me it would be the best day of my life, and I'd be damn sure to not be afraid of them. Makes me shake my F****** head and wonder what happened to all the good adult / mature animes (not hentai) like Cowboy Bebop, Berserk, Trigun, Outlaw Star, Big O, and the ever so classy Goldenboy.

I hope that somewhere some Japanese anime writer is reading this, making an anime with a male lead that actually isn't afraid to get laid...

When I start thinking about other stuff rather than watching the anime.
So when I get back to the anime, I have to skip back 1 min to 5 :P
It's not becaus the animes I watch is boring or anything, it's just that I have a lot to think about sometimes, and I think too much

When a show tries to make itself look more complex by using a series of cheap awful twists and not explaining them properly, the end result is me scratching my head and wondering WTF just happened.
Though it is not a good anime I would say 11eyes is a prime example of this.